High production of water-quenched filaments

ABSTRACT

Melt-spinnable thermoplastic polymeric filaments are melt extruded from at least one spinneret die plate having at least 25 spinning orifices per square inch of effective spinning area through an airgap of less than 1 inch into a liquid quench medium, for example, water. The surface tension of the quench liquid is maintained at least below 65 dynes per centimeter. The as-spun filaments can have a denier per filament in the range of about 4 to about 600. Polypropylene filaments processed in this manner have an X-ray diffraction pattern for the diffraction angle 2 theta in the range of 10*2 theta to 25* 2 theta characterized by two broad peaks located at about 15* 2 theta and about 21* 2 theta ; a crystal orientation pattern for an X-ray diffraction angle of about 14* 2 theta which exhibits a maximum at about the equator; a differential scanning calorimeter thermogram characterized by an exothermic peak at about 90* C.; and a crystallinity of less than 50 percent. The corresponding drawn polypropylene filaments have an equatorial Xray diffraction pattern for the diffraction angle 2 theta in the range of 10* 2 theta to 25* 2 theta characterized by a single peak located at about 15* 2 theta , and a crystallinity of less than 55 percent.

1111111211 States Patent [72] inventors Charles S. Hatcher; FOREIGN PATENTS Charles s both Granville, 918,722 2/1963 Great Britain 264/210 [21] Appl. No. 751,459 [22] Filed Aug 9, 1968 Primary Exammer-Jayll. W00 45 Patented Nov. 16,1971 Attorney-Young & Qulgg [73] Assignee Phillips Petroleum Company ABSTRACT: Melt-spinnable thermoplastic polymeric fila- [54] HIGH PRODUCTION OF WATER QUENCHED ments are melt extruded from at least one spinneret die plate FILAMENTS having at least 25 spmmngonfices per squareinch of effectiye 19 Chins, 9 Drawing Figs. spinning area through an airgap of less than 1 mch into ahquid quench medium, for example, water. The surface tension of [52] U.S.Cl 264/178, h quench li id i ai t i ed at least below 65 dynes per centimeter int. The as spun filaments can have a denier per filament in the [50] Field of Search ..264/176178; range of about 4 to about 00 polypropylene mamems 18/210 8 SS processed in this manner have an X-ray diffraction pattern for I 56] Ref (ed the diffraction angle 20 in the range of 1020 to 2520 characerences l terized by two broad peaks located at about 20 and about UNITED STATES PATENTS 2120; a crystal orientation pattern for an X-ray diffraction 2,324,397 7/1943 Hall 264/176 L angle of about 1420 which exhibits a maximum at about the 2,465,408 3/1949 Webb et al... 18/8 SS equator; a differential scanning calorimeter thermogram 2,820,252 1/1958 Koch 264/178 L characterized by an exothermic peak at about 90 C.; and a 3,095,606 7/1963 Scott 264/178 L crystallinity of less than 50 percent. The corresponding drawn 3,115,385 12/1963 Beck 264/178 L polypropylene filaments have an equatorial X-ray diffraction 3,134,833 5/1964 Ciproni et a1. 264/290 pattern for the diffraction angle 20in the range of 1020 to 3,485,906 12/1969 Oppenlander 264/178 L 20 characterized by a single peak located at about 15 20. and 3,487,142 12/ 1969 Johnson et a1. 264/176 L a cry tallinity o less than 55 percent.

37 ooo oo gi- 0 36 Q n 44 45 47 48 STAPLE CUTTER 1 42 1 STORAGE 43 m SURFACTANT 54 1 l I 1 l l 1 PATENTEnuuv 16 197i SHEET 3 [IF 5 FIG. 3

s m 4R 5 20R N EE R N U O WCG T TA T AE. A 2 2 SH CC 0 2 m B 44 9 2m 0 F 5 M E w HIGH PRODUCTION OF WATER-QUENCHED FILAMENTS The invention relates to method and apparatus for melt spinning filaments from synthetic polymers and the resulting products.

In the preparation of fibers from fusible polymers, it is customary to force the molten polymer through the orifices of a spinneret into a region where the temperature is lower than the temperature of the molten polymer. In the cooler region,.

the molten polymer sets up into filaments sufficiently firm to be drawn away continuously by a yarn forwarding device. conventionally, the molten polymer is spun through a spinneret having orifices spaced from each other by relatively large distances in order to keep newly formed filaments separated until they have congealed sufficiently to prevent their sticking together or coalescing. Productivity of yarn per spinneret under these conditions is low even at the highest practicable speeds of windup. Increased spinneret size can be achieved only to a limited extent due to the high pressures in the melt extrusion.

The large hole-to-hole spacing in conventional meltspinning spinnerets contrasts sharply with that used in solution spinning of viscose, where the holes are spaced so closely together that a tow of several thousand filaments can be spun at a single position. Owing to smaller plant space, smaller investment in equipment, and lower expense of labor and upkeep, this high density of spinneret holes permits preparation of fibers at a much lower cost than is possible with conventional melt spinning.

A second disadvantage of known melt-spinning practices concerns the difficulty of coupling the steps in yarn preparation. After a filament is spun, drawing is generally necessary in order to raise the mechanical properties of the filaments to an acceptable level. However, filament input to the drawing step usually proceeds at a rate necessarily different from the rate of filament output from the spinning step. For example, it may be necessary to draw the filament at a much lower rate than it is desirable to spin the filament. Under such conditions it is most efficient to interrupt the process of the yarn preparation, that is, to package the yarn temporarily after the spinning step for subsequent use in the drawing step. Even when it is possible to draw the yarn at a sufficiently rapid rate to allow its being used directly from the spinning step, the rate of yarn travel at the output from the drawing step often exceeds the capacity of currently available yarn-handling equipment.

This difficulty could be avoided by extruding the filaments slowly enough to allow the drawn filaments to be collected at a reasonable rate. But such an expedient would reduce the productivity of current spinning processes and would, therefore, be economically undesirable.

It has been proposed that melt spun filaments could be produced with a high filament population density per square inch of effective spinning area by utilizing a transversing air quench of at least 160 feet per minute within one inch of the spinneret die plate to solidify the filaments within two inches of spinneret die plate. However, no way of effecting this procedure without consolidation or marrying of the filaments has been found. Even were such a procedure to be proven feasible, it would be subject to the hazards of a failure in the air supply, undesirable variations in airflow velocity, uncontrolled air currents, vibrations in the equipment and the like.

In accordance with the invention it has been discovered that these difficulties can be avoided and that filaments can be melt spun in a high filament population density at commercial production rates by passing the melt spun filaments through an airgap of less than I inch, preferably less than one-half inch, into a body of quench liquid. It has also been found desirable to maintain the surface tension of the quench liquid below 65 dynes per centimeter. The resulting filaments have been found to be significantly different in their characteristics from the corresponding air quenched filaments.

Accordingly it is an object of the invention to provide an improved melt spinning process and apparatus therefor. It is an object of the invention to provide a high productivity melt spinning system. Another object of the invention is to provide a continuous in-line process for melt spinning filaments and treating the filaments, for example, by drawing and crimping. Yet another object of the invention is to provide new and useful melt spun filaments. Another object of the invention is to produce filaments having a larger denier per filament, and increased durability with the softness of smaller filaments, at high production rates.

Other objects, aspects and advantages of the invention will be apparent from a study of the specification and the appended claims to the invention.

In the drawings, FIG. I is a diagrammatic representation of a fiber spinning and treating system in accordance with one embodiment of the invention; FIG. 2 is a plan view of a spinneret die plate which can be employed in the system of FIG. 1; FIG. 3 is a graphical representation of the X-ray difiraction patterns of an as-spun, air-quenched polypropylene fiber and an as-spun, water-quenched polypropylene fiber; FIG. 4 is a graphical representation of the X-ray diffraction patterns of a drawn, air-quenched polypropylene fiber and a drawn, waterquenched polypropylene fiber; FIG. 5 is a graphical representation of the crystal orientation for an as-spun, air-quenched polypropylene fiber and an airspun, water-quenched polypropylene fiber; FIGS. 6, 7, 8 and 9 are graphical representations of the heat absorbed or generated by four fiber samples in excess of that which would have been observed in the absence of a phase change.

The process of the present invention is applicable to any melt spinnable synthetic organic thermoplastic polymer, for example, polyamides, polyesters, polyhydrocarbons such as polyethylene and polypropylene, polyurethanes, polyureas, vinyl polymers such as polyvinyl chloride, polyvinylidene chloride, and copolymers thereof, acrylic polymers such as polyacrylonitrile when sufficiently plasticized to render it fusible, copolymers of acrylonitrile, halogenated hydrocarbons such as polychlorotrifiuoroethylene, polyacetals, polyanhydrides, polyoxymethylenes, polyfonnals, polyethers, polythioethers, polysulfides, polythioesters, polysulfones, polythioureas, polythioamides, polysulfonamides, polyimides, and polytriazoles. The preferred group of polyamides comprises such polymers as poly( hexamethyleneadipamide), poly(hexamethylene sebacamide), poly(epsiloncaproamide), and the copolymers thereof. Among the polyesters that may be mentioned, besides poly(ethylene terephthalate), are the corresponding copolymers containing sebacic acid, adipic acid, isophthalic acid as well as the polyesters containing recurrent units derived from glycols with more than two carbons in the chain, e.g., diethylene glycol, butylene glycol, decamethylene glycol and trans-bis-l,4-(hydroxymethyl)- cyclohexane. For purposes of simplicity, a specific embodiment of the invention will be described in terms of a process for producing polypropylene fibers.

Referring now to the drawings, and to FIG. 1 in particular, polypropylene is convertedto its molten form in extruder 11 by a combination of external heat and generated heat caused by shear action, and passed through separate passageways to two melt spin metering pumps driven by motors l2 and I3. Molten polymer is passed at a metered rate from the metering pumps through screen packs to and through the spinneret die plates 14 and 15 to form a plurality of filaments at each die plate. The temperature of the extruded melt will generally be in the range of about 400 F. to about 650 F. for polypropylene, preferably in the range of about 450 to about 575 F. The extruder pressure will generally be in the range of about L000 p.s.i. to about 2,000 p.s.i. The spinnlng'speed can be increased by using smaller spinning orifices, increasing the temperature of the quench liquid, increasing the melt temperature accompanied by increasing the output rate per spinneret orifice by changing speed of metering pump. The filaments from spinneret die plates 14 and 15 pass through an airgap 16 into a body '17 of quench liquid, such as water, maintained in quench tank 18. The filaments from spinneret die plate 14 pass around a stationary guide pin 19 to a second stationary guide pin 21. Filaments from spinneret die plate pass around guide pin 21 and can be combined with the filaments from spinneret die plate 14 to form a tow or filament bundle 22. The tow 22 is withdrawn from quench tank 18 and passed through a tension ladder comprising stainless steel bars 28 and slotted pipes 29. The tension bars 28 create a constant tension source for the retarding rolls 31 to pull against, remove some quench liquid from the surface of the filaments, and align the filaments in a horizontal band to go through the retarding rolls 31 evenly. Pipes 29, which have transversa] slots therein, are connected by line 32 to vacuum pump 33 to remove excess water from the filaments.

A set of restraining or retarding rolls 31 are positively driven at a uniform constant rate to pull the filaments out of the quench bath and through the tension ladder. The rolls 31 also serve as a restraining device for draw rolls 34. Each of rolls 3!] can be heated, such as by steam or electrical heaters. A suitable temperature for rolls 31 for processing propylene fibers is in the range of about 230 F. to about 330 F. Heating the rolls 31 serves the dual purposes of completing the drying of the filaments and preheating the filaments for further conditioning in radiant heating oven 35.

The filament bundle is pulled through oven 35 by a set of draw rolls 34. With polypropylene, oven 35 can be designed for a residence time of l to 2 seconds to provide a drawing temperature of about 250 F. to about 300 F. The filaments are drawn generally in the range of 200 to 800 percent, and preferably in the range of 300 to 500 percent. it is presently desirable that the drawing take place as a neck-in at about 1 foot inside the oven 35 measured from the inlet end. A rolltype finish applicator 36 can be installed between oven 35 and draw rolls 34 to apply a finish material to the drawn filaments. Draw rolls 34 can be heated to a suitable temperature, for example, in the range of about 230 F to about 330 F. to at least partially dry the finish material and to anneal the drawn filaments by heat setting, which diminishes subsequent shrinkage.

The drawn filaments are passed around guide roll 37 and then between nip rolls 38 and 39 into stuffer box crimper 4]. The crimped tow is fed into a scray or J-box 42, which is provided with a pressure switch 43. The crimped tow is removed from scray 42 and passed around guide roller 44 by roller 45 which is driven by variable speed motor 46 responsive to pressure switch 43. The speed control can be either a continuously variable speed or multiple level speeds determined by pressure switch 43 acting as a level indicator. The crimped tow is then fed past guide roller 47 into staple cutter 48. The cut staple can be deposited in a storage unit 49. If desired, the crimped tow can be fed through a piddler into storage units and then subsequently fed to the staple cutter 48.

The length of the airgap 16 extending from the faces of spinnerets l4 and 16 to the upper surface of the body of quench liquid 17 has been found to be critical when processing a high population density of filaments from the spinnerets. in general, gap 16 has to be less than 1 inch in length when spinnerets 14 and 15 have at least 25 spinning orifices per square inch of effective spinning area. The term effective spinning area" designates the area enclosed by the outer line of spinning orifices in a pattern. Thus, with the spinneret die plate of FIG. 2, the effective spinning area is a circle having a radius v which extends to the outer periphery of the spinning orifices in the outer row. The spinning orifices should be separated from each other, both within a line such as the circular rows in FIG. 2 and between lines, by a distance d of at least 0.005 inch and preferably at least 0.01 inch, measured from the outer edge of one orifice to the nearest outer edge of an adjacent orifice. In order to achieve a high production rate in terms of pounds per hour, it is desirable that each spinneret die plate have at least 100 spinning orifices, preferably at least 500 spinning orifices. While the as-spun denier per filament will generally be in the range of about 4 to about 600, the process has been found to be particularly suited for producing filaments having an as-spun denier per filament in the range of about 60 to about 500. With a draw ratio in the range of2 to 6,

the drawn filaments generally have a denier per filament in the range of about i to about 300, preferably in the range of about l5 to about 100. Any greater length of the airgap at such filament population densities results in married filaments and other defects. The longer the airgap, the more sensitive the spinning operation becomes to air drafts. Baffiing can be provided to prevent or minimize any airflow around the airgap. On the other hand the airgap should be at least one-eighth inch to prevent contact of the quench liquid with the lower surface of the spinneret die plate and to prevent the radiant heating of the upper surface of the quench liquid by the die plate from being sufficient to cause localized boiling of the quench liquid. With filament population densities in the range of about 35 to about orifices per square inch of efiective spinning area, the air gap should be in the range of about one eighth inch to about one-half inch. in a presently preferred embodiment having a polypropylene filament population density in the range of about 40 to about 75 orifices per square inch of effective spinning area, an airgap distance of about three-sixteenth inch to about one-quarter inch has been found desirable. The airgap distance can be controlled by utilizing an adjustable weir 51 to separate the main portion of quench tank 18 from overflow section 52. A drain line 53 is connected to the bottom of section 52. instead of or in addition to an adjustable weir or its equivalent, means can be provided to effect relative movement of the quench tank 18 and the spinneret. A liquid level controller can be employed to maintain a desired level of quench liquid. If desired, the airgap can be filled with an inert gas, for example nitrogen, instead of air. Makeup quench liquid is passed through conduit 54 into quench tank 18. The temperature of the quench liquid in tank 18 can be maintained substantially constant by a temperature recorder controller 55 manipulating a valve 56 located in conduit 54 responsive to a comparison of the actual temperature of the quench liquid as indicated by temperature sensor 57 and the desired quench temperature represented by set point 58 on controller 55. The quench tank 18 can be provided with baffies, ifdesired, to minimize circulating currents and vibrations. The makeup quench liquid can be tap water at the available temperature or water which has been cooled or heated as desired.

It has also been discovered that the surface tension of the quench liquid becomes a significant factor with the high filament population densities. With a filament population density of at least 25 spinning orifices per square inch of efiective spinning area it is desirable that the surface tension be maintained below 65 dynes per centimeter. With a filament population density of at least 40 spinning orifices per square inch of effective spinning area, it is presently preferred that the surface tension of the quench liquid be maintained below 55 dynes per centimeter. To provide greater assurance of preventing marriage of adjacent filaments, to provide a greater margin of safety and to reduce the accuracy required, it has been found desirable to generally maintain the surface tension of the quench liquid below about 40 dynes per centimeter. A surface tension over 65 dynes per centimeter is sufficient at high filament population densities to cause lateral movement of the filaments in the airgap to the point where adjacent filaments adhere to each otherv The lateral movement also tends to introduce nonuniform stresses into the filaments. With a short airgap, a high surface tension can result in sufficient deformation of the liquid surface to cause contact of the quench liquid with the spinneret or sufficient proximity for the radiant heat to induce localized boiling. While it is possible to reduce the surface tension of the quench liquid by raising the temperature thereof, operation at higher quench temperatures increases the risk of localized boiling either by radiant heat from the spinneret or by conduction from the filaments entering the quench liquid. Accordingly, practice is to use a surfactant to decrease the surface tension. The surfactant can be passed through conduit 61 into conduit 54 wherein it is admixed with the quench liquid. The rate of addition of the surfactant can be controlled by ratio controller the presently preferred the water from the filament bundle as it passes through the ladder.

EXAMPLE I Filaments were produced in four different runs using a polypropylene having a melt flow (ASTM D l 238-62T. Condition L) of about 12. The processing data is set forth in table 1.

pie 1A. The solid line curve in F 10. 4 represents the equatorial X-ray diffraction pattern for water-quenched sample 28, while the dashed line curve in F 1G. 4 represents the equatorial X-ray diffraction pattern for air-quenched sample 18. The X- ray diffraction data indicates that both the as-spun, airquenched sample 1A and the drawn, air-quenched sample 1B exist in the monoclinic crystal form usually observed for crystalline polypropylene. The crystals in samples 1A and 18 have a length of approximately 70A. The X-ray diffraction patterns for the water quenched samples 2A and 28 indicate a degree of order which is neither amorphous nor crystalline but somewhere in between. One theory is that these samples contain small, distorted crystals in either the hexagonal or the TABLE I.-FIBER PROCESSING DATA Run I II III IV Quench system Air Water it Water Air Extruder barrel diameter, inches. r. 5 3 5 3% 3% Extruder tcmp., F r 475-525 450-525 450-575 101-506 Melt temp., F 500 485 430 4110 Spinnerct orifices 8 1, 000 1,000 70 Spinneret orifice diameter, mils 30 16 16 28 reduction rate:

Grams/minute. 208 Feet/minute. 85 Pack, mesh of screens. 10-150-411 Flow rate, g./min./hole 2. 97 Filament population density, orifices/square inch ESA... 4 Spin draw ratio 6 27. 5 Spun denier per filament 86 Air gap, inch Forced air quench column length, feet. 13 Total air column length, feet 32 Draw ratio 4. 8:1+1. 2:1 Draw temp, F 1 210/240 Final draw speed, f.p.m 492 Drawn denier per filament s Ratio of velocity olqncnched filament leaving the body of quench liquid to the velocity of the melt through the spinning orifices.

* 2-stagc.

Feed roll had a temperature of 240 F. while the draw 1 Feed roll had a temperature of 210 F. while the draw Run 1V is representative of a commercial process for spinning polypropylene filaments employing a conventional air quench of a transverse air velocity in the range of about to about 180 feet per minute. Runs II and III are representative of processing in accordance with the present invention. in the absence of a commercial process for producing air quenched polypropylene filaments having an as-spun denier filament above 100, run 1 was made to obtain comparative data for run 11. Runs 11 and III are continuous as illustrated in FIG. 1 through the crimper, whereas in runs 1 and IV the asspun yam was taken up on a package and then subsequently processed on a drawing machine. Joy dishwashing detergent was added to tap water in runs 11 and Ill to provide a quench liquid having a surface tension of less than 55 dynes per centimeter.

Samples 1A, 2A, 3A and 4A are representative of the quenched as-spun filaments of Runs 1, ll, Ill, and 1V, respectively. Samples 18, 2B. 3B and 4B are representative of the drawn filaments produced in Runs 1, 11, Ill and 1V, respectively, The characteristics of the samples are set forth in table 11.

TABLE lL-PHYSICAL PROPERTIES AND ORlE roll had a temperature of 200 F. roll had a temperature of 240 1'.

monoclinic form at a smaller degree of crystallinity than usual. with mean crystallite sizes being approximately 30A or less. This as-spun. water-quenched sample 2A has an X-ray difiraction pattern for the difi'raction angle 20 in the range of 10 20 to 25 20 characterized by having only two peaks. both broad. one being located at about 15 20 and the second peak being located at about 21 20. The peak located at about 15 20 has a width of about 3 20 at 80 percent of the peak height. The drawn. water-quenched sample 2B has an equatorial X-ray diffraction pattern for the diffraction angle 20 characterized by a single peak in the range of 10 20 to 25 20, the peak being located at about 15 26 and having a width of about 4 26 at 50 percent of the peak height.

in the as-spun, air-quenched fiber sample 1A, some preferential orientation with respect to the fiber axis is shown. in FIG. 5 the dashed curves represent the crystal orientation pattern for the as-spun, air-quenched sample LA at X-ray diffraction angles of 14. 1 26 and 16.9" 20. The crystal orientation pattern for the X-ray diffraction angle at l6.9 20 is a measure of the orientation of the 040 plane with respect to the NTAliON IARAMETE RS Denier Te- Elonga- Breaking Initial 5% secant Den- Crystal- Sonic Dire Melt per naeity tion strength modulus modulus sity li nity velocity frinpeak AIl filament (g.p.d.) percent (g.p.d.) (g.p.d.) (g.p.d.) (g./cc.) percent (kni./sec.) gence a0) f() 0.) (7.)

251. 0. 1230. 9. 31 14. 7 0047 65. 0 2. 23 002 351 053 164. 0. 56. 3. 15 84. 5. 46. 4 9074 68. 4 3. 57 030 7 802 165. .1. 236. 0. 74 740. 6. 22 0. 6 8877 43. 4 2. 07 001 247 024 164. 11. 8 62. 2. 98 64. 4. 80 48. 6 8055 53. 3 3. 55 029 7-15 734 106. 16. 86 8877 43. 4 2. 04 002 .222 048 163. 10. 26. 92 119. 6.43 30. 7 .8047 52. 3 3. l8 020 734 .731 166. 11. (l 86 .8073 55. 6 .1. 21 003 .341 076 162. J. 20. 4. 98 47. 7. 32 39. 5 006'.) 67. 8 3. 5 031 T03 826 170 15. (l

( Calculated from density values.

( De Vries optical orientation factor calculated from birefringence.

The equatorial X-ray difiraction pattern for waterquenched sample 2A is represented by the solid line curve in FIG. 3. while water-quenched line curve therein represents the equatorial X-ray diffraction pattern for air-quenched sam- Moseleys orientation factor calculated from sonic velocity at 18 (1.

75 plane with respect to the fiber axis.

in FIG. 5 the maximum at l for the l6.9 20 pattern for as-spun, air-quenched sample 1A indicates a slight preferential alignment of the monoclinic C axis (molecular axis) with respect to the fiber axis while the maximum at I =O for the 14.l 20 pattern for sample 1A indicates preferential alignment of the A axis parallel to the fiber axis. In contrast both the 14. 1 20 pattern and the l6.9 20 pattern for sample 2A have only equatorial maxima; thus some preferential orientation of the C axis only exists in this sample, if it is assumed that the sample is composed of small monoclinic crystals.

The percent crystallinity values, K, for these fibers were calculated from their densities, p, using the relationship:

where pam and pc are the densities of amorphous polypropylene and I percent monoclinic crystalline polypropylene. The values of pam=0.8535 and pc=0.9323 were taken from P. H. Geil, Polymer Single Crystals." Interscience I963). The results, reported in table II indicate that the drawn and undrawn water-quenched polypropylene filaments (samples 2A, 28, 3A and 3B) are significantly less crystalline than the corresponding air-quenched filaments. In general, the as-spun, water-quenched polypropylene fibers produced in accordance with the invention have a crystallinity of less than 50 percent, whereas the corresponding drawn water-quenched fibers have a crystallinity of less than 55 percent.

Average molecular orientation parameters were determined for these fibers by birefringence, and also by sonic velocity. The latter method makes use of the relationship:

where Cu is the sonic velocity in an unoriented specimen and C is that for the test specimen. This relation has been proposed by Moseley, J. Appl. Polymer Sci. 3, 266 (I960). Moseley showed that the sonic velocity was independent of crystallinity below the glass transition temperature, Tg, and therefore measures the total molecular orientation (amorphous plus crystalline) at these temperatures. The value of Cu for polypropylene at l 8 C., a temperature well below Tg, was found to be L796 km./sec. by Sheehan, Wellman and Cole, Textile Research Journal, 626 July I965). Therefore our sonic velocity measurements were made at l8 C., and 1.796 km./sec. was used in equation l to calculate a.

The optical orientation factor f is defined as:

f A/Amax for crystalline polypropylene by R. .l. Samuels, J. Polymer Science A, 3, L741 (I965).

These values were used together with the density crystallinity values in table II to calculate the optical orientation factors for these samples. These parameters should also measure the total molecular orientation of the fiber.

The orientation parameters reported in table II agree quite well for the drawn 60 dpf fibers. However, there is significant disagreement between the optical and acoustical values for the undrawn samples. This may be due to the fact that the birefringence technique measures the average birefringence throughout the cross section of the filament while the sound wave is propagated along the length of the filament and, if there is a skin-core effect, i.e., an orientation gradient in the radial direction of the fiber with highest orientation in the skin, the acoustical method might give a higher orientation factor than the optical method because of faster sound wave travel along the higher-oriented surface. Both methods indicate that the air-quenched samples are significantly more highly oriented than the water-quenched samples in the undrawn state.

The two orientation factors for the drawn 20 dpf samples are in excellent agreement with each other, and indicate that the air-quenched sample 48 is more highly oriented than the water-quenched sample 38.

Thermal analysis runs were performed on all samples using the Perkin-Elmer Difi'erential Scanning Calorimeter DSC) at a scanning rate of 10 C./min. The enthalpy changes associated with phase changes in the polymer were calculated from these runs and those for the as-spun samples IA, 2A, 3A and 4A are presented graphically in FIGS. 6-9, respectively. The ordinate of these graphs, dh/dT, is defined as the heat, in calories, absorbed or generated by the sample per gram per degree C in excess of that which would have been observed in the absence of a phase change. Negative values of dh/Jl' indicate an exothermic phase change such as crystallization while positive values indicate an endothermic phase change such as fusion. The temperature at which the maximum in the endothermic peak occurs is conventionally referred to as the melting peak. These values are given in table II. Since small or distorted crystals will melt at a lower temperature than larger or more perfect crystals, the width of the endothermic peaks may be used as a measure of the crystallite distribution relative to size and perfection. The peak widths at one-half of the maximum are presented in table II.

All of the DSC curves show the normal melting behavior of monoclinic polypropylene. However, there are certain significant efi'ects present in several of the curves which should be discussed. The undrawn water quenched process fibers shown an exothermic transition over the range from 60 C. to I20 C. with the exothermic peak being at about Cv This has been attributed to conversion from the quenched state to the monoclinic" by .l. A. Gailey and R. H. Ralston, SPE Trans. 4, 29 (1964). This transition was not present on any of the airquenched samples.

The tenacity. elongation and modulus were measured on all samples with the exception of the two undrawn 86 dpf samples. These results are presented in table II. Tensile properties are usually not measured on undrawn fibers since they give no indication of the properties of the finished product. However, the properties of the 240 dpf undrawn fibers were measured in order to compare the two spinning processes without the complication of the drawing step. These results indicate that the initial modulus and the 5 percent recant modulus for the airquenched sample llA are significantly higher than those for the water-quenched sample 2A. This is consistent with the higher orientation and higher crystallinity for the airquenched sample. The higher breaking strength for air quenched sample 1A, i.e. higher tenacity at break based on the denier at break, indicate that a stronger fiber is produced by the air-quench process.

The data show that the tensile properties of the drawn 20 dpf fibers. samples 38 and 4B, are significantly different. The tenacity and moduli of the air-quenched sample 48 are higher than those of the water-quenched sample 38 and the elongation of the air-quenched sample is lower than the waterquenched sample. These results are consistent with the higher orientation factors for the air quenched fibers. The lower initial modulus of the water quenched process fiber indicates that this sample will have approximately 30 percent lower stiffness than the air-quenched sample since the flexural rigidity or stiffness of a round fiber, i.e. the couple required to bend the fiber to unit radius of curvature, is proportional to the initial tensile modulus and the 4th power of the radius of the fiber. See Physical Properties of Textile Fibers" by Morton and Hearle pg. 378, Mechanics of Deformable Bodies" by Sommerfelt pg. 297 of Formulas for Stress and Strain" by Roark, pg. 94.

EXAMPLE I] A run with polypropylene having a melt index of about 12 was made with a water quench spinning system of the type illustrated in HO. 1, utilizing a 2-inch extruder and a single spinneret die plate. The die plate contained 752 holes having a diameter of 20 mils, with a filament population density of 65 spinning orifices per square inch of effective spinning area. The airgap distance was one-half inch. Tap water having a temperature of about 70 F. and a surface tension of about 72 dynes per centimeter was utilized as the quench liquid. The asspun, water-quenched filaments had a denier per filament of about 262 and was withdrawn from the quench tank at a rate of about 47 feet per minute. The yarn was then cold drawn to a denier per filament of about 116. Initially, a considerable number of the filaments combined in the airgap. A surfactant was then added to reduce the surface tension of the quench water below 40 dynes per centimeter and the problem of filament marriages was eliminated.

A second run was made with the same equipment except the quenched filaments were withdrawn from the quench tank at a rate of about 125 feet per minute to produce as-spun filaments having a denier per filament of about 62.5. Again the use ofa surfactant to maintain the surface tension of the quench liquid below 40 dynes per centimeter avoided the marriage of filaments.

A third run was made omitting the surfactant, with a quench water temperature of 170 F. and a surface tension of about 63 dynes per centimeter. No significant marriages of filaments were noted.

EXAMPLE Ill A run with polypropylene having a melt index of about 12 was made in a water quench spinning system of the type illustrated in FlG. l, utilizing a Zia-inch extruder and one spinneret die plate, having 1,000 spinning orifices with a diameter of 16 mils, and a filament population density of 51 spinning orifices per square inch of effective spinning area. The extruder die temperature was 575 F. for a melt temperature of about 490 F. and a production rate of about 123 pounds per hour. The rolls 3! were operated at 230 F. and I feet per minute. Tap water containing sufficient surfactant to produce a surface tension of less than 40 dynes per centimeter at an operating temperature of about 105 F. was utilized as the quench liquid. When the airgap exceeded 1 inch, the filaments combined to render production impractical if not impossible. When the airgap was between 1 inch and one-half inch some instances of filament marriages were noted. When the airgap was reduced to the range of one-eighth inch to one-fourth inch, the problem of marriages was eliminated.

Reasonable variations and modifications are possible within the scope of the foregoing disclosure, the drawing and the appended claims to the invention.

What is claimed is:

l. A process for forming fibers which comprises extruding a melt-spinnable thermoplastic polymer in molten form through the spinning orifices of at least one spinneret die to form a plurality of filaments, each said spinneret die having at least I00 spinning orifices with at least 25 spinning orifices per square inch of effective spinning area, passing said filaments through an airgap into a body of quench liquid, said airgap extending from the face of said spinneret to the surface of said body of quench liquid and having a distance less than 1 inch, withdrawing the thus-quenched filaments from said body of quench liquid and maintaining the surface tension of said quench liquid below 65 dynes per centimeter.

2. A process in accordance with claim I wherein said polymer is polypropylene.

3. A process in accordance with claim 1 wherein the number of orifices per square inch of effective spinning area is in the range of about 35 to about 100.

4. A process in accordance with claim 1 wherein the quenched filaments withdrawn from said body of quench liquid have a denier per filament in the range of about four to about 600.

5. A process in accordance with claim 4 further comprising drawing said withdrawn quenched filaments to achieve a denier per filament in the range of about one to about 300.

6. A process in accordance with claim 1 wherein the number of orifices per square inch of effective spinning area is in the range of about 40 to about 75, the withdrawn quenched filaments have a denier per filament in the range of about 60 to about 500; further comprising drawing said withdrawn quenched filaments to achieve a denier per filament in the range of about 15 to about 100.

7. A process in accordance with claim 6 wherein the total number of orifices per spinneret die is at least 500, further comprising collectively passing the at least 500 drawn filaments in the form of a tow through a crimping zone to crimp said tow.

8. A process in accordance with claim 7 further comprising cutting the thus-crimped tow into staple.

9. A process in accordance with claim 6 wherein said thermoplastic polymer is polypropylene.

10. A process in accordance with claim 6 further comprising maintaining the surface tension of said quench liquid below 55 dynes per centimeter.

11. A process in accordance with claim 6 wherein said airgap distance is in the range of about one-eighth inch to onehalf inch.

12. A process in accordance with claim 11 wherein said quench liquid is water, and wherein the surface tension of the water is maintained below about 40 dynes per centimeter by the addition of a surfactant to the water.

13. A process in accordance with claim 12 wherein said airgap distance is in the range of about three-sixteenths inch to about one-fourth inch.

14 Apparatus comprising at least one substantially horizontally positioned spinneret having at least spinning orifices per spinneret with at least 25 spinning orifices per square inch of effective spinning area, means for extruding molten melt spinnable polymer downwardly through said spinning orifices to form a plurality of filaments, means for positioning a body of quench liquid immediately below said spinneret so that the distance between the lower face of said spinneret and the upper surface of said body of quench liquid is less than 1 inch and means for withdrawing the quenched filaments from said body of quench liquid.

15. Apparatus in accordance with claim 14 wherein each spinneret has at least 500 spinning orifices with at least 35 spinning orifices per square inch of effective spinning area.

16. Apparatus in accordance with claim 14 further comprising means for removing quench liquid from said body of quench liquid in accordance with the level of the upper surface of said body of quench liquid, means for adding relatively cool makeup quench liquid to said body of quench liquid in accordance with the temperature of said body of quench liquid, and means for adding at least one surfactant to said body of quench liquid in an amount which is responsive to the amount of makeup quench liquid added to said body of quench liquid to thereby maintain the surface tension of said body of quench liquid below 65 dynes per centimeter.

17. Apparatus in accordance with claim 14 wherein the number of orifices per square inch of effective spinning area is in the range of about 35 to about 100.

18. Apparatus in accordance with claim 17 further comprising means for maintaining the surface tension of said body of quench liquid below a desired value.

19 Apparatus in accordance with claim 18 wherein said means for maintaining comprises means for adding a metered amount of surfactant to said quench liquid. 

2. A process in accordance with claim 1 wherein said polymer is polypropylene.
 3. A process in accordance with claim 1 wherein the number of orifices per square inch of effective spinning area is in the range of about 35 to about
 100. 4. A process in accordance with claim 1 wherein the quenched filaments withdrawn from said body of quench liquid have a denier per filament in the range of about four to about
 600. 5. A process in accordance with claim 4 further comprising drawing said withdrawn quenched filaments to achieve a denier per filament in the range of about one to about
 300. 6. A process in accordance with claim 1 wherein the number of orifices per square inch of effective spinning area is in the range of about 40 to about 75, the withdrawn quenched filaments have a denier per filament in the range of about 60 to about 500; further comprising drawing said withdrawn quenched filaments to achieve a denier per filament in the range of about 15 to about
 100. 7. A process in accordance with claim 6 wherein the total number of orifices per spinneret die is at least 500, further comprising collectively passing the at least 500 drawn filaments in the form of a tow through a crimping zone to crimp said tow.
 8. A process in accordance with claim 7 further comprising cutting the thus-crimped tow into staple.
 9. A process in accordance with claim 6 wherein said thermoplastic polymer is polypropylene.
 10. A process in accordance with claim 6 further comprising maintaining the surface tension of said quench liquid below 55 dynes per centimeter.
 11. A process in accordance with claim 6 wherein said airgap distance is in the range of about one-eighth inch to one-half inch.
 12. A process in accordance with claim 11 wherein said quench liquid is water, and wherein the surface tension of the water is maintained below about 40 dynes per centimeter by the addition of a surfactant to the water.
 13. A process in accordance with claim 12 wherein said airgap distance is in the range of about three-sixteenths inch to about one-fourth inch. 14 Apparatus comprising at least one substantially horizontally positioned spinneret having at least 100 spinning orifices per spinneret with at least 25 spinning orifices per square inch of effective spinning area, means for extruding molten melt spinnable polymer downwardly through said spinning orifices to form a plurality of filaments, means for positioning a body of quench liquid immediately below said spinneret so that the distance between the lower face of said spinneret and the upper surface of said body of quench liquid is less than one inch and means for withdrawing the quenched filaments from said body of quench liquid.
 15. Apparatus in accordance with claim 14 wherein each spinneret has at least 500 spinning orifices with at least 35 spinning orifices per square inch of effective spinning area.
 16. Apparatus iN accordance with claim 14 further comprising means for removing quench liquid from said body of quench liquid in accordance with the level of the upper surface of said body of quench liquid, means for adding relatively cool makeup quench liquid to said body of quench liquid in accordance with the temperature of said body of quench liquid, and means for adding at least one surfactant to said body of quench liquid in an amount which is responsive to the amount of makeup quench liquid added to said body of quench liquid to thereby maintain the surface tension of said body of quench liquid below 65 dynes per centimeter.
 17. Apparatus in accordance with claim 14 wherein the number of orifices per square inch of effective spinning area is in the range of about 35 to about
 100. 18. Apparatus in accordance with claim 17 further comprising means for maintaining the surface tension of said body of quench liquid below a desired value.
 19. Apparatus in accordance with claim 18 wherein said means for maintaining comprises means for adding a metered amount of surfactant to said quench liquid. 